Aluminium alloy having low coefficient of expansion



Patented Oct. 10, 1950 PATENT OFFICE ALUMINIUM ALLOY HAVING LOW COEFFI- CIENT F EXPANSION Horace Campbell Hall and Marcus Alan Wheeler, Derby, England, assignors to Rolls-Royce Lim ited, Derby, England No Drawing. Application August 24. 1946, Serial No. 692,934. In Great Britain March 10, 1944 Section 1, Public Law 690, August 8 1946 Patent expires March 10, 1964 The object of this invention is an aluminium alloy which will have a low coefficient of expansion but will have at the same time-.a-good strength (particularly as regards the qualities of proof stress and creep), have a good hardness, and be easy to cast.

It is known that a high content of silicon in aluminium alloys reduces the coefficient, of expansion. Known alloys, however, of this type have certain disadvantages which it is the object of our invention to avoid.

According'to our invention we make an alloy of the following elements in the following pro portions:

Silicon per cent of 111501101 10.0-15.0

'8' Claims; ((175-143) The alloy can be prepared in a manner familiar to foundrymen, for instance, to molten aluminium are added rich alloys of the various elemerits. The magnesium, maybe added in metal-l 0.31per cent and can be up to 0.55 per cent though a maximum of 0.45 per cent is preferred.

.Sodium, if present, is added just prior to cast-v ing.

Nickel 0, v For foundry purposes the alloy can be made. Copper and Silver together and and ingotedand then remelted for making castcluding at 1east0.05 per cent of ings m the normal mannereach 0 5. 1 An example of our alloy was prepared of the Manganese do 0.15-0.45 following m Magnesium d O 0.07-0.55 13.0 per cent Iron and zinc (as impurities) if any 8:2 3:5

not exceeding per cent of each 0,6. 0.30 per ce t Aluminium the remainder. H d v i 3; 333% Iron and zlnc a j presentas impuriq1es25 Titanium 0.025 53; iitperived mainly fromasilicon-rich in commercial alumlmum or secondaryaalumm- Oalclfim 0. 04 per cent alloy used in preparation. ium but each should preferably not exceed 0.35 g. i per cent. Up to atotal of each of 0.6 percent arigf f 9 per can may be permitted but if the ironcontent 'exgg i gg f ceeds 0.35 per cent the manganese content should be between 0.25 per cent and 0.45 per cent.

The following elements may be added as refiners up to 0.15 per cent of any one and 0.35 per cent of the elements in all: Boron, calcium, cerium, V chromium, cobalt, lithium, molybdenum, niobium, potassium, sodium, tantalum, titanium, tungsten, vanadium. and zirconium.

Of these the most important is sodium which may be added in ,known manner. just before cast-' ing. About 0.1 per cent is the preferred amount; It results in theiproductionpf a: fine aluminiumsiliconeutectic. The amountsgiven are those added to the alloy of whichsome maybe lost. 1

' Fluxes containing alkaline fluorides and chlorides may be used and havesomemodifying ef-" fect. p

The preferred constitutionof the alloy is as This when'sand cast, cooled, heat treated by heating for 12 hours at 160 C. and allowedto cool, gave the following approximate test results:

Brinell hardness, '73

Maximum stress, 12.5 tons per square inch 0.1% proof stress, 9.0 tons per square inch Elongation, 2.5%

Coeificient of expansion from 20-150, C. 0.000019" per C.

The above coeflicient of expansion may be compared with that of awell known alloy No. in the R. R. series which for similar temperatures is 0.000023" per C.

At 200 C. after soaking at that temperature for half an hour the alloy gave the following results:

follows: Maximum stress tons 12.1 Silicon; 1.5 13.2 percent 0.1% proof 9.0 Nicke1 .25- .45 e, ent' Y i8 253 Elongation "p r c nt" 1ver 5- per'cen Iron .0 .35 per cent These results 1ndicate that ohysicalproperties tggfigggi :5 g5; are well maintained up to 200 C. j Calcium .0 .15 Del cent The above example of our alloy when chill cast 9 :8 5:; 3:3,? and aged 12 hours at 160 C. gave the following .07- .30 ti Z1- .ti r t: Mmesmm --i .07- .45 BS? 23% f8 3th 52301355 esiul S Aluminium the n ra r Brinell hardness 87 Such small contents of thorium and/orberyl- Maximum stress tons per square inch 14 lium not exceeding 0.1 percent in total maybe 0.1% proof stress do 10.5 added with advantage, Elongation per cent 3.0

Tests have also been made on specimens cut from a sand cast cylinder head, cast in the alloy, weighing about 200 pounds including gates, runners and risers. The size of the head measured approximately 42 x 8 x 7 /2 inches and the one flat face of the casting was formed by a thin metal plate on which was placed the sand mould containing a number of intricate cores.

After fettling the head was aged for 14 hours at 165-170 C.

The composition as determined by chemical analysis was as follows:

Per cent by weight Silicon 12.10 Nickel 0.38

Copper 0.46 Silver 0.36 Magnesium 0.20 Iron 0.50 Manganese z 0.42 Zirconium 0.12 Sodium 0.03 Titanium 0.03

Calcium 0.02 Aluminium The remainder Tensile tests on test pieces cutout of casting:

(a) From thick section from face:

Maximum stress tons/sq. in 16.65 Yield point do 10.75 Elongation per cent 6.0 Reduction of area do 5.5 Brinell hardness Q. '79

(D) From thick section in. from face:

Maximum stress tons/sq in 13.9 Yield point do 10.2 Elongat on per cent 3.8 Reduction of area do 5.0 Brinell hardness 76 (c) From heavy section 4 inches from face:

Maximum stress tons/sq. in 12.0 Yield point d 8.6 Elongation .s per cent" 3.0 Reduction of area do 3.0 Brinell hardness 66 Fatigue tests on specimens cut out of a casting:

Rotating cantilever alternating bending tests-i- (a) At room temperature:

- -4.55 tons/sq. in for 40$ 10 reversals (b) At 150 0.:

- -4.30 tons/sq. in. for 40 reversals The following figures for Youngs modulus were obtained on specimens from the cylinder head casting:

At 18 0. 11.6 X 10 lbs. At 200 C.210.6X 10 lbs.

1Creep.-The following creep tests were made on specimens cut from a sand casting of similar composition to above. Under 9.0 tons/sq. in. stress applied as a continuous load in bending at. 150 'C., the rate of creep strain is only 0.3 10- inches/hour between the 400th and 500th hours under the applied load. Under exactly similar conditions, that is 9 tons at 150 C., the figure obtained on a chill-cast modified silicon-aluminium alloy in general commercial use 4 was 4.0x 10- inch/hour between 400th and 500th hours under load. The presence of silver confers better properties, particularly under creep at elevated temperatures without seriously affecting the coefiicient of expansion.

The alloy may be given solution treatment up to 540 C. with or without subsequent agein at about C. for 24 hours or about 6 hours at 180 C. High temperature heat treatment, however, is not usually advisable for large or complicated castings due to liability to heat stressing and distortion.

When high temperature solution treatment is given the magnesium and copper content should be near the maximum in order to get the best mechanical properties.

The alloy can be used in the forged state. in which expression we include all types of mechanical working but in this case the silicon content should not exceed 12.5%. The usual heat treatments may be given.

What we claim is:

1. An aluminium alloy formed of the following elements in the following proportions:

.Per cent of the whole Silicon 10.0 15.0

Nickel -0.1 0.8 Copper and silver together and ineluding at least 0.05 per cent of each 0.35- 1.0 Manganese 0.15- 0.45 Magnesium 0.0'7- 0.55 Aluminium the remainder.

, 2. An aluminium alloy formed of the following elements in the following proportions:

Per cent of the whole Silicon 10.0 l5.0

Nickel 0.1 0.8 Copper and silver together and ineluding at least 0.05 per cent of each 0.35- 1.0 Manganese 0.15- 0.45 Magnesium 0.07- 0.55 Aluminium the remainder together with the usual impurities including up to 0.6% of iron and up to 0.6% of zinc.

3. An aluminium alloy formed of the following elements in the following proportions:

Per cent of the whole Silicon 10.0 15.0 Nickel 0.1 0.8 Copper and silver together and including at least/0.05 per cent of each 0.35- 1.0 Manganese 0.15- 0.45 Magnesium 007- 0.55 Up to 0.15% of boron, 0.15% of calcium, 0.15% of cerium, 0.15% of chromium, 0.15% of cobalt, 0.15%-

of lithium, 0.15% of molybdenum,

0.15% of niobium, 0.15% of potassium, 0.15% of sodium, 0.15% of tantalum, 0.15 of titanium, 0.15

of tungsten, 0.15% of vanadium,

and 0.15% of zirconium, and up to 0.35% in total of boron, calcium,

cerium, chromium, cobalt, lithium,

molybdenum, niobium, potassium,

sodium, tantalum, titanium, tungsten, vanadium and zirconium.

A u i ium, the mainder.

N 4. An aluminium alloy formed of the following elements in the following proportions:

Per cent of the Whole Silicon 10.0 -15.0

Nickel 0.1 0.8 Copper and silver together and including at least 0.05 per cent of each 0.35- 1.0

Manganese 0.15-0.45 Magnesium 0.07- 0.55

5. An aluminium alloy formed. of the following elements in the following proportions:

Per cent of the whole Silicon 10.0 l5.0

Nickel 0.1 0.8 Copper and silver together and including at least 0.05 per cent of Thorium and beryllium in total up to 0.1 per cent.

Aluminium the remainder together with the usual impurities including up to 0.6% of iron and up to 0.6% of zinc.

7. An aluminum alloy formed of the following elements in the following proportions:

Per cent of the whole Silicon 10.0 15.0

Nickel 0.1 0.8

Copper and silver together and including at least 0.05 per cent of each 0.35- 1.0 Manganese 0.15- 0.45 Magnesium 0.07- 0.55

Up to 0.15% of boron, 0.15% of calcium, 0.15% of cerium, 0.15% of chromium, 0.15% of cobalt, 0.15% of lithium, 0.15% of molybdenum, 0.15% of niobium, 0.15% of potassium, 0.15% of sodium, 0.15% of tantalum, 0.15% of titanium, 0.15% of tungsten, 0.15% of vanadium, and 0.15% of zirconium, and up to 0.35% in total of boron, calcium, cerium, chromium, cobalt, lithium, molybdenum, niobium, potassium, sodium, tantalum, titanium, tungsten, vanadium and zirconium.

Thorium and beryllium in total up 0.1 per cent.

Aluminium the remainder.

8. An aluminium alloy' formed of the following elements in the following proportions:

Per cent of the whole Silicon 10.0 -15.0

Nickel 0.1 0.8 Copper and silver together and including at least 0.05 per cent of each 0.35- 1.0

Manganese 0.15- 0.45

Magnesium 0.07- 0.55

Up to 0.15% of boron, 0.15% of calcium, 0.15% of cerium, 0.15% of chromium, 0.15% of cobalt, 0.15% of lithium, 0.15% of molybdenum, 0.15% of niobium, 0.15% of potassium, 0.15% of sodium, 0.15% of tantalum, 0.15% of titanium, 0.15% of tungsten, 0.15% of vanadium, and 0.15% of zirconium, and up to 0.35% in total of boron, calcium, cerium, chromium, cobalt, lithium, molybdenum, niobium, potassium, sodium, tantalum, titanium, tungsten, vanadium and zirconium.

Thorium and beryllium in total up to 0.1 per cent.

Aluminium the remainder together with the usual impurities including up to 0.6% of iron and up to 0.6% of zinc.

HORACE CAMPBELL HALL. MARCUS ALAN WHEELER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,354,953 Pritchard Apr. 19, 1932 1,879,748 Horsfield Sept. 27, 1932 1,947,121 Bonsack Feb. 13, 1934 2,280,174 Stroup Apr. 21, 1942 

1. AN ALUMINIUM ALLOW FORMED OF THE FOLLOWING ELEMENTTS IN THE FOLLOWING PROPORTIONS: 